Exploring The Human-Ape Paradox - Todd Preuss, Nina Jablonski, Lyn Wadley

we are the paradoxical ape bipedal naked large brain long the master of fire tools and language but still trying to understand ourselves aware that death is inevitable [Music] yet filled with optimism we grow up slowly we hand down knowledge we empathize and deceive [Music] we shape the future from our shared understanding of the past carter brings together experts from diverse disciplines to exchange insights on who we are and how we got here [Music] an exploration made possible by the generosity of humans like you [Music] welcome to my archive of half-read books uh i'm grateful for the opportunity to speak to you about brain differences between humans and apes this is a daunting task given how much our knowledge of the subject has grown recently so i can't treat the subject comprehensively what i'll do instead is focus on the association cortex the classic regions prefrontal posterior parietal temporal cortex and their connections with each other because these seem particularly pertinent to possible human cognitive and behavioral specializations as well as to neurocognitive disorders i'm also going to talk about the intersections between brain studies and genomic research as this is a wave of the future what's driving this new knowledge to a large extent the development and maturation of comparative neuroimaging and comparative genomics one thing we've known for a long time is that human brains are bizarrely large more than three times the size of those of african apes of similar body size such as male chimpanzees or female gorillas this enlargement accelerated about two and a half million years ago with the appearance of the genus homo what accounts for this increase in brain size mainly the expansion of association cortex there are lots of old graphs and tables supporting this claim but a picture is worth a thousand words and mri excels at nothing so much as generating pictures with mri you can map the density of intracortical myelin across the cortical gray matter and this turns out to be very revealing it's important to bear in mind that myelin isn't only found in white matter of course there's a lot in the white matter where it covers axons but the gray matter of the primary sensory and motor areas like primary visual cortex primary motor and sensory somatosensory cortex primary auditory cortex and their neighboring secondary areas also have a lot of well-myelinated fibers in these maps those regions code as red or green well association cortex tends to be very poorly myelinated and codes blue and the human picture is strongly dominated by blue now you can get a more detailed picture using mri morphometrics which involves determining where and by how much you have to stretch virtually chimpanzee cortex to make it match certain landmarks in human cortex when you do this it's apparent that large segments of prefrontal temporal and posterior parietal cortex are three to four times larger in humans than in chimpanzees whereas most of the primary and secondary areas enlarge much less interestingly the primary auditory cortex of humans stands out as an exception so what happened to the organization of association cortex as it enlarged well one mode of change was repurposing evolution modified some existing areas to to support new functions including language so for example we have good evidence that homologues of the classic language areas of broca and wernicke exist in apes and in other non-human primates species that don't have language for broca's area the evidence consists of commonalities in the location of the area with respect to other areas aspects of connectivity and non-linguistic motor functions such as control of forelimb and orofacial movements the homologous areas in humans of course also support language but wait there's more this region is also involved in the organization of complex hierarchically organized actions and perhaps it's biased towards the right hemisphere in this regard so the region is activated during tool making including the fashioning of paleolithic tools with the more complex aschulean tools like hand axes yielding more activation than making of the earlier simpler uldavan tools surprisingly perhaps it's also involved in social cognition including such high level functions as reasoning about mental states aspect of theory of mind in fact it's part of the social brain network so how did evolution modify broca's area to support human specific functions one possibility is that its connections with other regions were altered we can investigate this using diffusion neuroimaging a set of techniques that allow us to trace fiber pathways through the white matter between other between areas it's based on the propensity of water molecules to diffuse along rather than across fiber tracts because the myelin sheaths that surround fibers are fatty and thus hydrophobic and we can use diffusion imaging to reconstruct the several homologous major fiber bundles that connect distant areas in humans and also in apes and in fact in other non-human primates now long before the development of neuroimaging we knew from gross dissections that broca's area and the frontal lobe was connected with wernicke's area and the temporal lobe by a fiber bundle called the arcuate fasciculus and one might expect that the evolution of language that with the evolution of language there would be some differences in the areas interconnected by the arcuate in humans and apes and comparative diffusion imaging studies indicate that indeed there are in humans the arcuate fasciculus has much stronger connections with the middle temporal gyrus than in chimpanzees or in macaques for that matter that's interesting because the middle temporal gyrus is known to harbor semantic representations including representations of word meanings now that we know what parts of human cortex expanded in human evolution we can take advantage of our newfound knowledge of evolutionary changes in gene structure and gene expression to see how the two are related you may have heard of these so-called human accelerated regions of the genome these are dna segments that by by definition underwent the most extreme or numerous changes in sequence in the human lineage now most of these aren't genes in the conventional sense because typically they don't code for proteins but rather are dna segments that regulate the expression of nearby genes in the brain human accelerated regions regulate the expression of numerous genes at least some of which are involved in synaptic formation and dendritic development not surprisingly perhaps mutations of these so-called har-associated genes disrupt cognition and social behavior where are the har associated genes expressed in the cortex well pretty much everywhere but they're expressed most strongly in the higher order association regions in humans now although humans and chimps both show greater expression of homologous higher associated genes in higher order association cortex in the higher order regions that are available for comparison in the cycan code database humans show a more than two-fold expression enhancement compared to chimpanzees or macaques now we don't know what structural and functional consequences these expression differences have but given the involvement of har-associated genes and regulating synaptic and dendritic formation it seems likely they play a role in crafting the internal information processing architecture of cortical association areas i want to turn now to brain plasticity this is of course a well-known feature of gray matter less well-known is white matter plasticity that is experience driven changes in the physical properties of white matter fibers that affect the strength and velocity of the signals they carry these changes occur throughout the lifespan and really this should come as no surprise since the neurons in the gray matter have to continually evaluate and weigh information from their various inputs which arrive through the white matter and the waiting should vary with experience there are now several landmark studies of white matter plasticity but to take an example learning to make alternating left and right hand movements requires communication speed communication between the two hemispheres which results in changes in the fiber tract that connects them namely the corpus callosum how do you modify signal strength in the white matter in part at least by modifying the amount of myelin that surrounds axons this is orchestrated by a symphony of molecular signals passing between neurons and the cells that make myelin sheaths namely oligodendrocytes in this way neuronal signals can remodel myelin sheaths and thus change the weighting of their signals given this dimension of plasticity along with the range of skills cognitive motor and otherwise that humans acquire and continue to modify over the course of a lifetime it's pertinent to ask whether humans differ from apes in the genetics of oligodendrocytes and they do many more oligocyte genes underwent expression changes in humans than in chimpanzees since their lineages separated interestingly in humans there's a set of co-expressed oligodendrocyte genes that have allelic variants associated with schizophrenia and other neurocognitive disorders the normal functional consequences of these oligodendrocyte gene expression changes remain to be explored but there's reason to think that some of them at least relate to the plasticity of cortical systems and notably human brains are more variable individually in their morphology than our chimpanzee brains one line of evidence suggesting that our brains are more plastic so the material i've covered today suggests a number of follow-up questions for example what about the genetic control of the non-uniform expansion of association areas we can ask about the genetic control of changes in cortical connectivity and physiology we can ask about genetic control of plasticity and also about the disease consequences of human neural and genetic specializations these are pretty deep questions about human nature fortunately we now have tools to address these questions and many like them so researchers can access neuroimaging data online including data about chimpanzees you can inquire about gene sequence and gene expression changes again online and if these don't meet your needs you can request suitable brain tissue from a variety of sources and do your own work so i want to emphasize the unique value of the information about chimpanzees represented here for understanding human brain evolution and human disease because much of this came from investigations done at yerkes in the past and there's no new chimpanzee research being carried out there so this is our treasure trove for understanding human brain specializations greetings and welcome to this lecture which is part of the symposium on the human ape paradox a fascinating topic and to me there is no more fascinating part of this paradox than skin most people don't think about skin between humans and apes as being that interesting because nobody's really talked about it very much but in the next few minutes you'll see that it's really interesting naked skin or mostly naked skin is one of the hallmarks of modern humans and has probably probably been in our lineage for oh about two million years what is the significance of this why did it evolve in the first place and what do we do with it once it has evolved this is a really fascinating evolutionary story that i've been really privileged to work on for about the last 20 years it's pretty clear that our skin is very different from that of our closest living relatives the chimpanzees when the chimpanzee genome was studied and published in 2005 we realized just how significant this difference was many people expected us the humans to be really different from chimps in genes related to our brain or our musculature but it turns out that we were most divergent from chimpanzees in our skin and specifically in the surface or epidermis of our skin so this really delighted me because i knew that human skin was remarkably special in many of its properties if we look at this wonderful graphic that i call the hairy timeline of human evolution we can see that humans diverged from our closest living relatives chimpanzees about seven and a half million years ago in other words that's when we shared a common ancestor and our common ancestor probably had lightly pigmented skin covered with dark hair but if we fast forward up to the emergence of our own members of the genus homo around 2 million years ago we see that something else is going on in the evolution of skin our skin is becoming considerably less hairy and is becoming more pigmented if we look at this superb specimen of an early member of our genus discovered on the western shores of lake turkana in kenya we see really a very modern looking human skeleton with very long legs relatively short arms this was a really active striding sweating biped naked skin is one of the hallmarks of modern humans and we evolved naked skin almost certainly at about the time of the emergence of the genus homo as we became more and more active and needed to liberate more body heat from the surface of our bodies hair and heavy coats of hair like our chimpanzee relatives have is very good at insulating us but it also impedes the evaporation of sweat and the cooling of the surface of the body and so we basically lost most of our body here this tiny hairs are still there but effectively we are mostly hairless except for a few parts of our body including the surfaces of our head so in early members of the genus homo we had a mostly naked skin that is the primary interface with the environment and wow this is a completely different kind of of primate than we have seen before and we'll just see how different this is when humans lost most of their body hair we lost many of the abilities that we used to have as apes in being able to show our emotions not only through posture and facial expressions but also through erecting our hair these very agitated chimpanzees show this this very very effective emotional display what happened when we lost most of our hair this is a really good question well we know that humans and apes are very visually oriented so what visual signals sort of replaced this ability to raise the hair to show fear and anger and emotional motivations as it were well we can speculate that one of the things that developed in our lineage was a heightened ability to express our emotions through our facial expressions and so we see very finely differentiated facial muscles and an even greater focus on the skin of the face so very very mobile and expressive faces and on the skin itself we see that blushing becomes a salient social signal in everyone regardless of skin color the effusion of the skin the suffusion of the skin with blood in at times of heightened emotion especially embarrassment becomes a very very important social signal that other people take cognizance of and we begin with our beautiful naked skin and our cultural abilities to decorate ourselves this is something that no ape does humans decorate themselves lavishly and in many ways they use their skin as a canvas for self-expression the piece of ochre on the right side is retrieved from the blomboss cave archaeological site in south africa it is over 70 000 years ago it was probably used to decorate people as well as the surfaces of rock shelters we are not only visual we are highly color sensitive as visually oriented primates and so we end up developing very colorful modes of decorating our naked skin and we become very very attuned to slight differences in color of the skin in these two beautiful examples the man on the right shows a very beautiful south american pigment that is used in body painting especially facial painting and the woman on the left from burma shows these extremely fine tattoos signaling of intent signaling of identity signaling of meaning through the decoration of the skin is extremely important in humans and is really universal one of the few things that we can see in virtually every culture that has ever been studied we see combinations of different kinds of of skin based decoration scars tattoos sometimes mixed with body painting and other forms of body art but this naked skin not only is a beautiful canvas for self-expression is naked and exposed to the sun we evolved in tropical habitats with very high solar loads so how did we deal with hot sun without the protective covering of hair on our bodies when we look at the intensity of ultraviolet radiation on the earth's surface we can see that in the areas of africa close to the equator here where i'm pointing where our lineage differentiated where early members of the genus homo lived and early members of homo sapiens lived we have very high levels of ultraviolet radiation in this very equatorial and dry area these pink and red areas are very high areas of ultraviolet radiation the green and gray areas concomitantly much lower these turn out to be really important because as humans disperse from mostly being tropical living to living all over the world they're adapting to different levels of ultraviolet radiation and the primary way in which they adapt to these levels is through changes in skin pigmentation when we reconstruct the likely appearance of that ancestral member of the genus homo we reconstruct the male and the female to have mostly naked skin covered with sweat glands and imbued with dark protective pigmentation melanin pigmentation turns out to be a remarkably good natural sunscreen here we can see a diagram of the eu melanin molecule it's a long polymer molecule that provides exquisite protection against ultraviolet radiation it shows up as dark it absorbs most visible light but it's a remarkable neutralizer of reactive oxygen species that are formed when ultraviolet radiation impinges on the skin and it absorbs ultraviolet radiation itself so it's a remarkable remarkable pigment that is used by humans in their evolution as well as by myriad other mammals and other vertebrates that live under intense uv light so when we look at our hairy timeline of human evolution and go up to two million years ago we see the the evolution of functionally naked potentially very sweaty skin with dark pigmentation and as we begin to move to early members of our own species homo sapiens that is evolving in africa around 300 000 years ago we see that those people are evolving increasingly darkly pigmented skin and this is what we see in all of humanity from the beginning from our very origins as modern humans about 300 000 years ago until some small groups began to leave the african continent around 80 000 years ago all humans were darkly pigmented imbued with marvelous eu melanin pigmentation that protected them from the harmful effects of ultraviolet radiation so what happened in human evolution the man on the left has this beautiful natural sunscreen in his skin but what about the woman on her right in order to understand her skin we need to understand the pace and nature of dispersals of early humans into the non-tropical parts of the world so if we go back to our ultraviolet radiation map and think about how early homo sapiens may have moved through the old world and eventually into northern parts of eurasia as well as eventually into northern parts of the new world we basically see a story of tropical people going out of the tropics at least some of them and some of them re-entering tropical latitudes this has tremendous implications for the evolution of skin pigmentation because it turns out that although most ultraviolet radiation is harmful some of it turns out to be useful in effect essential the dispersal into high latitudes involved both biological and cultural adaptations and both turn out to be remarkably important in the evolution of homo sapiens as populations disperse especially into high latitudes away from the equator we can really describe that in the ancestors of western europeans and eastern asians we see a loss of pigmentation this lightly pigmented skin is very good at actually scavenging ultraviolet radiation photons in order to begin the process of making vitamin d in the skin as i said most ultraviolet radiation is harmful but some uv radiation short wavelength uvb is necessary to produce vitamin d in the skin as people dispersed into higher latitudes it was actually essential for their health and reproductive success for them to have less eu melanin sunscreen in their skin hence my use of the word depigmentation so we can really think about skin pigmentation as an evolutionary compromise and this is one of the great distinctions between apes and humans is that humans homo sapiens one species that comes in a remarkable range of skin colors that are quite finely tuned to ultraviolet radiation levels people who live closer to the equator in areas of high uv have emphasized protection against intense solar radiation whereas people living closer to the poles have emphasized that photosynthetic ability to make more vitamin d in the skin these three men are beautiful examples of darkly pigmented skin in three evolutionarily distinct lineages of modern people all closely related genetically but they have been distinct from one another in that they diverged from a common ancestor and then dispersed into different parts of the old world at different times what's so interesting about them when we look at their skin pigmentation genes is that they diverge in many genes even though they look the same the skin pigmentation genetic mechanisms for making dark pigmentation or tanned skin are actually distinct in both lightly pigmented skin and darkly pigmented skin there are multiple genes that contribute to the same phenotype or the same appearance under similar solar conditions many genes can work to produce the same effect under the same environmental conditions this is really interesting so the guy from india on the right and the guy from africa on the left actually both have darkly pigmented skin but for slightly different genetic reasons and similarly these guys all share different characteristics of their bodies when we look at the shape of their heads their noses the texture of their hair and other features of their face and bodies we can see that they look remarkably different from one another even though they all have darkly pigmented skin and this is really important to recognize that skin pigmentation evolved mostly independently of other traits and so it can't be used as a unique marker of group identity or racial identity so here we are this beautiful beautiful multi-colored species one of the things that modern humans didn't anticipate in their early evolution was that we would be moving all over the world mixing and mingling with one another we have these beautiful theaters of human evolution and human interactions not always good-natured ones because of our penchant for visual observation for creating differences between one another on the basis of fine perceived differences but mostly we are a harmonious beautiful multi-colored species capable of tremendous amounts of cutaneous self-expression through our beautifully naked skin i want to thank very much carter for the invitation to participate in this session and my husband and collaborator george chaplin for continuing support and discussion my research assistant tess wilson for assistance in all all practical matters with my research and many many people and organizations who have funded my research and who have discussed these results over the years i hope you'll get in touch with me with your questions thank you activities involving the lighting and use of fires separate hominins from other primates indeed many of the innovations attributed to early humans were dependent on pyrotechnology in a hunter-gatherer context fire is mostly associated with domestic uses such as cooking heating social interactions and protection from predators importantly though fire enables some technical tasks and products like ash were exploited in a variety of ways from at least 300 000 years ago fire gave humans the edge over other primates where and when did this begin [Music] fire simply obtained from burning branches or coals originating in wildfires must first be distinguished from fires started from dry wood tender and some means of making sparks for ignition more than a million years ago fire seems to have been obtained expediently from natural sources and then used briefly at sites like kubifora in east africa and vondavac and swat krantz in south africa the ephemeral burned layers in vondevac are in a dark area about 30 meters from the cave entrance all the evidence suggests that this fire was transported from a natural source such as a lightning strike that set the grassland alight it was then used in the cave but the fire could not be curated and maintained for long certainly homo erectus the lucky occupant of this cave seems not to have been able to make fire from scratch and probably collected it from wildfires nonetheless we know that homo erectus had an enriched diet compared with earlier hominins because relative to them homo erectus had large brains but small teeth and guts this physique may have come about through increased meat consumption when hunting became efficient the occasional cooking of food may have contributed to the new brain gut ratio perhaps this is so but we don't have firm evidence yet habitual use of fire is suggested by the central placement of a hearth in the late lower paleolithic site kesem cave israel somewhere between four hundred and twenty and two hundred thousand years ago before the arrival of anatomically modern humans not only were kesem hominins cooking on fire but based on artifact use traces and botanical remains they seem to have used ash as a preservative for various foods and perhaps also for high preparation it appears that hominins were able to make fire at wool by this time early homo sapiens fossils date from about three hundred thousand years ago at jebel urhut in north africa and slightly after this at florist bud in south africa the start of the african middle stone age coincides roughly with the appearance of homo sapiens by a hundred and seventy seven thousand years ago homo sapiens was founded in the leo cave in israel suggesting that the earliest homo sapiens migrations out of africa may have begun two hundred thousand years ago by that time fire was a regular part of human technology kesem is not the only example of early exploitation of the byproducts of fire by 227 000 years ago at border cave south africa modern humans put ash to good use as i shall shortly explain border cave is large and it was extensively excavated in the last century the present excavations sample small areas exposed by previous archaeologists here in the 227 thousand-year-old member five white ash there are several superimposed ashy layers implying repeated use of fire and probably the ability to make it at will there are also ephemeral tracers of solicified grass the grass is essentially fossilized in slightly younger members we find burned rhizomes presumably from using fire for cooking and i shall discuss this shortly the plant material from the early bedding was studied using a scanning electron microscope as well as phytolith analysis both methods revealed anatomical features like leaf blade structures and bilobate short cells prickles and stomata these identify the border cave plant fragments as grass from the panacoidy subfamily panicum maximum still grows prolifically outside the cave although the oldest bedding is ephemeral now it may once have looked like better preserved grass bedding in some of the younger occupations within the stone edge sequence of border cave people often placed grass on ash occasionally this ash was derived from older grass bedding that may have been burned to clean the site but sometimes grass was placed on raked wood ash chemical analysis of sediments can identify ash and sometimes its origin can be distinguished at border cave marine wagesap conducted on-site ftir analyses and we could therefore be certain that ash was indeed used underneath grass bedding ash provides a clean dry insulating surface but ethnographies report further that ash repels crawling insects and various parasites ash supposedly blocks their breathing and biting apparatus and dehydrates them the two images at the top of the screen show how the grass bedding may have been made the two images below this show how we experimented with 30 brown ticks placing them in a circle of ash within a sealed container those ticks that breached the ash wall were smothered in the powder and moved with difficulty ash may thus have some efficacy in preventing bites from parasites that endanger people's health border cave people seem to have employed several techniques for keeping pests away sandra lennox used the wood anatomy of charcoal found on the 227 thousand-year-old bedding to identify the camphor bush tarkananthus the smoke from this aromatic species is used by modern rural communities to repel insects maasai herdsmen in east africa still make bedding from tarkananthus leaves and also burn its wood we found more than 60 charred rhizomes of underground plants in border cave occupations dating between 170 and 120 000 years ago some rhizomes were presumably buried and lost while being roasted in hot ash they were all from the same species and their morphology matched that of a small hypoxis cooking makes food more digestible and easier to chew than when raw it facilitates peeling rhizomes and it enhances the glucose availability of starchy plants hypoxis was identified largely from the anatomy of the rhizome we found raphaites which are calcium oxalate crystals and xylem vessels particularly useful for identifying the rhizomes people dug the rhizomes in the field then transported them and firewood along the steep cliff back to the cave they could easily have prepared and eaten the rhizomes where they were unearthed but they did not the cooking of rhizomes in the cave was a planned activity with the reward deliberately delayed presumably in order to share the food at the home base the process tells us something about the social practices and the cognitive attributes of these early humans at classy's river in the southern cape quartzite rocks may have been used to add cooking because they were ridden by repeated heating and fire unidentified underground storage organs were cooked here more than a hundred thousand years ago other aspects of pyrotechnology are surprisingly early by 164 000 years ago people appear to have discovered the transformative power of heating certain salicious rocks careful heating of some rocks and minerals makes them especially suitable for napping heat treatment is particularly beneficial for pressure flaking at pinnacle point sulcrete was heated from the time of the earliest occupations heat treatment was also observed at lombos where bifacial points were carefully crafted from silkwete an aspect of pyrotechnology that has absorbed much of my research time has been the production of glue a single component product and adhesive a compound product the success of manufacturing fixative pastes is dependent on controlled heat something that can be achieved by understanding the properties of various woods ramen and eds spectra revealed hematite and carbon in the adhesive on a cebudu point 72 000 years old the adhesives on sixty four thousand year old tools comprise plant resin and okapada compounds gas and liquid chromatography identified coniferous resin while ramen confirmed the presence of hematite i wanted to know whether the recipes were created with knowledge of the properties of the ingredients i therefore manufactured some glues and adhesives with and without powdered ochre and heated them gently to dry them they were then used to join wooden strips that were later pulled apart by a universal testing machine compound adhesive containing a mixture of ochre and gum is stronger than gum alone this suggests that people knew that ochre was a successful loading agent and they did not simply choose the ochre for its color people at blomboss made ochre rich paint a hundred thousand years ago probably by using the same sort of technology demonstrated for adhesive manufacture cebudus occupants created a type of tempera paint thousands of years later as shown in this brief review that favors african examples fire technology was already quite well developed before 200 000 years ago close to the origin of our species people could produce fire at wool and they used fire ash and smoke from medicinal plants to maintain clean pest-free camps modern hunter-gatherer camps have fires as focal points people regularly sleep alongside them and perform domestic tasks in social contexts the earliest homo sapiens groups seem to have behaved similarly among the tasks they performed around fires were some fairly sophisticated creations of compound mixtures to enable the assembly of composite tools and weaponry [Music] you

Channel: University of California Television (UCTV)

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Keywords: Todd Preuss, Jablonski, Wadley, CARTA, evolution, skin, neurodevelopment, early fire-use

Id: iN7VoN-DumU

Length: 52min 50sec (3170 seconds)

Published: Wed Nov 11 2020